Method of forming electrostatographic toner particles



United States Patent O 3,338,991 METHOD OF FORMING ELECTROSTATO- GRAPHIC TONER PARTICLES Michael A. Insalaco and Carl F. Clemens, Webster, and Myron James Lenhard, Rochester, N.Y., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York No Drawing. Filed July 2, 1964, Ser. No. 380,080 11 Claims. (Cl. 264-7) This invention relates in general to electrostatography and in particular to a method for the production of electrostatograp'hic materials.

Electrostatography is perhaps best exemplified by the process of xerography as first described in US. Patent 2,297,691 to C. F. Carlson. In this process, a photoconductor is first given a uniform electrostatic charge over its surface and is then exposed to an image of activating electromagnetic radiation which selectively dissipates the charge in illuminated areas of the photoconduc-tor while charge in the non-illuminated areas is retained thereby forming a latent electrostatic image. This latent electrostatic image is then developed or made visible by the deposition of finely divided, electroscopic marking material referred to in the art as toner, on the surface of the photoconductor, which marking material conforms to the pattern of the latent electrostatic image. The visible image may then be utilized in a number of diverse ways. For example, the image may be viewed in situ on the photoconductive insulator, fixed in place on the photoconductive insulator or transferred to a second surface such as a sheet of paper and fixed in place thereon as desired depending upon whether the photoconductive insulating material is reusable as is the case with amorphous selenium photoconductive insulators or non-reusable as is the case with particulate zinc oxide-binder film type Xerographic plates.

Although the original Carlson patent describesdeveloping the latent electrostatic image by dusting it with various powders such as lycopodium, gum copal, cumarone-indene resin, various powdered dyes and the like, many other developing materials and techniques have been devised since that time. Some of the development techniques include powder cloud development as described in US. Patent 2,918,900 to Carlson, liquid spray development as described in US. Patent 2,551,582 to Carl son, immersion development as described in US. Patent 3,010,842 to Ricker, loop development as described in Us. Patent 2,761,416 to Carlson and donor development as described in US. Patent 2,895,847 to Mayo. However, it is more than likely that the commercial development technique most widely used today is the technique known as cascade development as described in US. Patent 2,618,552 to Wise. This latter development technique is carried out by rolling or cascading across the latent electrostatic image bearing surface, a developing mixture composed of relatively large carrier particles, each having a multiplicity of electrostatically adhering fine marking particles, known as toner particles, on its surface. As this mixture cascades or rolls across the image bearing surface, the toner particles are electrostatically deposited on the charged portion of the image and not on the uncharged background areas of the image. In addition, toner particles accidentally falling on these non-image areas are physically removed therefrom by the electrostatic attraction of carrier particles which pass in close proximity to these unbound toner particles. The results of this devel opment process is an excellent background-free copy of the electrostatic image made up of the toner particles electrostatically clinging to the image surface. As a general rule when any one of these development processes is used 3,338,991 Patented Aug. 29, 1967 with a reusable xerographic plate, such as an amorphous selenium xerographic plate, the toner particle image is transferred to and fixed on a second layer such as a paper sheet in contact with the toner image by adhesive transfer or by electrostatic transfer as described in US. Patent 2,576,047 to Schaifert. After the image is transferred from the surface of the amorphous selenium xerographic plate, the plate surface may be cleaned and it is then ready for reuse in a subsequent xerographic cycle. The toner resins are usually thermoplastics, selected to have melting points significantly above any ambient temperatures which might be encountered (generally running above F.) and these are fixed to the paper in most cases by radiant heat fusing.

Most other electrostatographic techniques use the above-described or similar development methods employing the same type of marking material or toner, and differ only in the mode of forming the latent electrostatic charge pattern which is developed. (See for example US. Patents 2,576,047 to Schati'ert and 3,064,259 to Schwer-tz). In another technique for example, in US. Patent 3,081,698 to Childress, a conductive screen with a plurality of apertures which define the image area to be reproduced is spaced opposite a conductive backing elec trode and a potential is applied between this backing electrode and the screen such that when finely divided electrostatographic toner particles smaller than the apertures in the screen are applied to the surface of the screen opposite the backing electrode, the electrostatic field set up by the potential source causes the particles to move through the apertures in the screen to form a toner image .on the backing electrode in the configuration of the apertures on the screen. Various surfaces may be interposed between the screen and the backing electrode so that the :particle image may be intercepted and formed on such insystems is that they employ the lines of force from an electric field to control the deposition of finely divided, marking material or toner on a surface, thus forming an image with the toner particles.

In addition to the developing powder or toner materials described in the original Carlson Patent No. 2,297,691 a number of additional toner materials have been developed especially for use in the newer development techniques including the cascade technique described immediately above. Generally speaking, these new toner materials have comprised various improved resins mixed with different pigments such as carbon black. Some exemplary patents along this line include US. Patent 2,659,670 to Copley which describes a toner resin of rosin-modified phenol-formaldehyde, U.S. Reissue 25,136 to Carlson which describes a xerographic toner employing a resin of-polymerized styrene, and US. Patent 3,079,342 to Insalaco describing a plasticized copolymer resin in which the co-monomers are styrene and a methacrylate selected from the group of butyl, isobutyl, ethyl, propyl, and isopropyl.

In the past, these toners have generally been prepared by thoroughly mixing the heat softened resin and pigment to form a uniform dispersion as by blending these ingredients in a rubber mill or the like and then pulverizing this material after cooling to form it into small particles. Most frequently, this division of the resin-pigment dispersion has been made by jet pulverization of the material. Although this technique of toner manufacture has produced some very excellent toners, it does tend to have a rather wide range of particle sizes in the toner particles. Although the average particle size of toner made according to this technique generally ranges between about 5 and microns, individual particles ranging from sub-micron in size to above 20 microns are not infrequently produced. In addition, this technique of toner production imposes certain limitations upon the material selected for the toner because the resin-pigment dispersion must be sufficiently friable so that it can be pulverized at an economically feasible rate of production. The problem which arises from this requirement is that when the resin-pigment dispersion is sufficiently friable for really high speed pulverizing, it tends to form even a Wider range of particle sizes during pulverization including relatively large percentages of fines and is'frequently subject to even further pulverization or powdering when it is employed for developing in xero graphic copying apparatus. All other requirements of xerographic developers or toners including the requirements that they be stable in storage, non-agglomerative, have the proper triboelectric properties for developing, form good images, do not film or soil the selenium xerographic plate and have a low melting point for heat fusing are only compounded by the additional requirements imposed by this toner forming process.

Other techniques of toner production are known even including spray drying toner from a dyed resin solution as described in U.S. Patent 2,357,809 to Carlson (page 2, column 2). Even though this technique can produce small well-shaped particles, these particles tend to bleed dye and to be unstable under the influences of light, heat and/or aging. Since toners are subjected to many of these infiuences either during imaging or afterwards, they are not always acceptable for all uses.

Now, in accordance with the present invention, it was suggested that an insoluble pigment be suspended in the resin solution to make up the liquid for spray-drying of toner so that the final particles would be colored, and although it was thought that this would result in the production of much free pigment after drying, it was tried with the result that no free pigment was produced, but only well-colored particles containing both resin and pig ment. Also in accordance with the present invention, there is provided a new and improved method of xerographic toner production which is greatly simplified and is still capable of producing xerographic toner particles with very significantly improved uniformity of particle size. Toner produced according to this new method has .also been found to have a unique spherical shape with greatly enhanced developing capabilities especially in cascade systems where the developer rolls across the plate during development. In addition, it has been found that this new method of xerographic toner production is capable of forming a xerographic toner of extremely small particle size. Both the uniformity of particle size and the fineness of particle size which may be achieved in this new method of toner production have gone to produce an electrostatographic toner with extremely high resolution capabilities and which may be used in virtually any electrostatographic technique including those described above. The ultimate resolution capability of any xerographic system or other electrostatographic technique is limited by the largest toner particles which are included in the batch of xerographic toner being utilized to develop the latent electrostatic image regardless of the particular development technique employed. Thus even when an optical system and xerographic plate are capable of producing extremely high resolution latent electrostatic images, the overall system resolution is destroyed if the latent image is developed with a xerographic toner containing particles of a size substantially larger than the dimensions of any part of the latent image. Accordingly, xerographic toner produced according to the new method of this invention is superior in many other respects for the production of high resolution xerographic images. First, it removes the restrictions imposed on the toner materials by the pulverizing particle forming process. Secondly, it is capable of producing extremely small particle size xerographic toner and thirdly, it significantly narrows the particle size range of the toner produced thus significantly reducing or completely eliminating any random particles of much larger than average size which might be included in a xerogr-aphic toner produced by conventional techniques.

Basically, the technique of this invention consists in adding a suspended, insoluble pigment to a solution of the desired toner resin and then spray drying it under controlled conditions so that the relatively volatile solvent is driven off and the resin precipitates out of solution forming finely-divided particles including the pigment. Contrary to expectations, when a suspended pigment was used, all of the pigment was found to be encapsulated in the spray dried toner particles and no free pigment was produced by the process. The pigment is present in the toner in sufficient quantity to cause it to be highly colored whereby it will form a clearly visible image when it is used in xerographic development. In the usual case where a xerographic copy of a typed letter or printed document or the like is desired, the toner colorant may be a black pigment such as carbon black or other minutely divided carbonaceous pigment. Where other colored toners are required, other organic or inorganic pigments maybe employed as colorants. Since the pigment is insoluble in the toner resin solution, it must be uniformly suspended therein prior to the final spray drying step. So as to avoid the problem of blending the pigment into suspension directly in the resin solution, the pigment is first blended in the solvent and then this suspension is added to the resin solution to complete the mix. Although pigment suspensions in some solvents are commercially available (for example a suspension of carbon black in ethyl acetate is available from the Columbian Carbon Company) these suspensions may be readily prepared by various techniques such as ultrasonic blending with a Sonifier ultrasonic blender produced by Branson Instrument Company or by ball milling from about 1-4 hours in a vibrating ball mill,- with the resin solution. Since these two latter techniques do not always provide a suspension which is stable for more than a few hours, with some pigments it is generally desirable to :add a surfactant to the suspension if it cannot be blended with the resin solution and spray dried within a relatively short time. Even with good suspending agents, some of the pigment suspensions such as carbon black in ethyl acetate are quite vulnerable to coagulating influences. Accordingly, it is desirable to add these suspensions to the resin solution slowly and with careful stirring to blend the two together uniformly. By carefully controlling the amount of resin in solution, the amount of colorant in solution or suspension and the size of the droplets formed in the spray drying process, the size of the final toner particle produced after drying is completed may be controlled. This result is achieved because the amount of liquid solvent driven off by evaporation in each droplet of the same size will be equal, thus leaving an equal weight of resin and colorant solids to form the final toner particle. Since this resin which precipitates out of solution in any one droplet to form the toner particle by encapsulating the pigment included in that particle acts in effect as a binder, it is generally desirable to maintain the size of the pigment particles, blended into the resin solution as small as possible and always well below the size of the final toner particle to be produced, so that it is well encapsulated within the resin and so that the pigment will never tend to increase the size of any toner particles beyond their desired diameter. Since the toner particles will generally be produced in sizes ranging from about .5 to about 25 microns the pigment should preferably not exceed a diameter of about .1 micron and wherever possible should be smaller as this not only contributes to the uniformity of end product coloration but also tends to create a more stable suspension of the pigment prior to the spray drying. In

fact, commercially available carbon black pigments ranging in size from about 7-0 millimicrons in diameter down to about 200 millimicrons in average diameter were used to good effect in the formation of spray dried toners as described more fully in the examples which follow.

Although any one of many known resinous developing materials which are electroscopic in nature and which form coherent spheres when they come out of the solution may be used to form the resin solution it has generally been found that electrically insulating, water insoluble, thermoplastic or unset thermosetting, synthetic polymers including for example those described in the patents to Copley, Carlson and Insalaco, referred to above, form toners having many highly desirable properties, especially for use in automatic copying machines where heat fusing is employed to fix the toner image to the copy sheet. In the event that the final toner is to be employed in a process which uses other toner image fixing techniques, the resins employed may be modified accordingly.

Thus, for example, Where the toner image is fixed by solvent vapor fusing as described, in US. Patent 2,776,907 to Carlson or by the application of an adhesive overcoating, the resin employed need not necessarily be softenable at relatively low temperatures. Since, as described above in the brief introductory description of the process, the resin is first placed in solution, the primary requirement to be observed in this selection of the resin is that it be soluble in an inexpensive commercially available solvent and thus many thermoplastics and unset and partially unset thermosetting resins can be used. Suitable materials include for example, vinyl-type polymers and copolymers such as styrene and its homologs vinyl naphthalene, acrylics and methacrylics as well as alkyds, epoxies and others. Any one of the commercially available organic solvents may be used including chlorinated solvents such as trichloroethylene or methylene chloride, aromatic solvents such as toluene, aliphatic solvents such as naphtha, ketones such as methyl ethyl ketone or esters such as ethyl acetate or amyl acetate. In some instances, the selection of the solvent must be made with care so as to assure that all resin components are soluble in it. Thus, for example, where the resin consists of a copolymer of styrene and a methacrylate plasticized with polyvinyl butyral, a common solvent for the plasticizer and the copolymer should be used such as ethyl acetate or amyl acetate.

In the following examples, the unit employed for spray drying was the Bowen Laboratory spray dn'er manufactured by the Bowen Engineering Corporation North Branch, New Jersey. This unit is a lab size conical drier with concurrent air flow and has an interchangeable atomizing head mounted near the top of the drying chamber and fitted inside the drying :air distributor ring. Any

one of a number of well known atomizing heads commonly employed in spray drying apparatus may be employed in the apparatus such as centrifugal or swirl-type pressure nozzles, pneumatic or two fluid atomizing nozzle in which a jet of the liquid to be atomized is disintegrated as it leaves the nozzle by a high velocity gas stream, a supersonic nozzle in which the liquid is atomized by supersonic vibrations or an impingement atomizer in which the liquid stream is atomized by impingement against a solid surface. The atomizer most widely used in the following examples was of the spinning disc variety in which the liquid is broken up by vdischarging it at a high velocity from the periphery of a rapidly rotating disc. This type of atomizer is preferred where, as here, a suspended pigment is included in the liquid being atomized since other atomizing devices frequently erode during atomization under high speed friction with these solids. With any of the atomizers the size of the final toner particle produced is determined by different variables. Thus, for example, with pneumatic or two fluid atomization it was found that the two variables which had the principal effect on particle size of the final toner produced are: viscosity of the liquid atomized and air velocity of the Solution Ooncen- Mean particle Trial Number tration in perdiameter in centage weight] microns volume Holding all other variables constant higher atomization pressure in the pneumatic nozzle decreased the mean diameter of the final toner particles produced as indicated in the following table:

Run Number Atomization Mean diameter Pressure, p.s.i.g. in microns With the spinning disc atomizer it was again found that viscosity of the resin solution had a marked effect upon the average particle size produced when all other process variables are maintained constant with mean particle size in microns dropping off very rapidly from about 20 microns at a solution viscosity of 4 centipoises and increasing slowly above 20 microns as solution viscosity increases above 4 centipoises. The disc radius and speed are interrelated factors which effect the centrifugal force on the liquid at the periphery of the disc which in turn is a major variable affecting the droplet size produced by the atomizer. Since atomization is a highly complex and imperfectly understood phenomenon the best results probably may be obtained by following the empirical data given herein to produce specific particle sizes.

Once the liquid has been atomized to the proper droplet size, it moves through the drying air in the spray drying chamber until the solvent is driven off by evaporation leaving the resin in the form of a single spherically shaped toner particle encapsulating the colorant. This evaporation is hastened by the high surface to mass ratio of the atomized droplets and the warmth of the drying air. The time during which these droplets are held in suspension in the drying air is referred to as the dwell time. The maintenance of correct drying air temperature is important to effective operation of the system because the drying' air is required to drive off the solvent in each droplet by evaporation during the dwell time, while at the same time the particles must be cool enough as they leave the drying air chamber so that they are not tacky enough to stick to the sides of the collecting apparatus or to agglomerate in the collecting device. It has generally been found that with most of the desirable polymers this result may be achieved by maintaining an input drying air temperature which is just above the minimum required to effect evaporation of the solvent during the dwell time. This result is produced with these polymer-solvent systems because evaporation of the solvent after the droplets make initial contact with the heated air, tends to cool the droplets so that they are no longer tacky as they leave the drying chamber even when the initial drying air temperature makes them tacky. If one of the less volatile solvents is employed, this result sometimes requires a longer dwell time for the droplets or the use of smaller droplets with higher solids concentrations so that the solvents will dry off faster even with lower temperatures in the drying chamber. With most of the conventional thermoplastic resins which are employed in toners and which are intended for heat fusing in xerographic processes, the problem of excessive tack in toner particles leaving the drying chamber may be avoidedby keeping the exiting air at about 135 F. or lower as these resins do not soften until they achieve a temperature well above this level. Where for some reason a resin is employed which becomes tacky at low temperatures, relatively close to room temperature, or where dwell time in the drying air chamber is so short as to require higher than average entry air temperatures, it may be desirable to quench the dried toner particles as they leave the drying chamber with a stream of cold air to reduce their tackiness and prevent their agglomeration and sticking in the collector. This step, however, is unusual and is not required with most of the conventional materials. The output of the spray drier is collected in a cyclone-type collector from which the final dried particles may be taken at the end of the process.

In most cases, the pigment in a final toner particle should not exceed 25% by weight as larger percentages tend to impede free flow of the powdered toner and to make fixing of the toner difiicult because of the lower percentage of thermoplastic in each particle. It also has been observed that although toner particles of other shapes may be employed, spherically shaped particles are most desirable because they produce better images and move through developing devices more freely. It has been found that this shape particle is produced with greatest regularity when the spray dried liquid from which it is made has a viscosity below about 500 centipoises and preferably about 100 centipoises. Viscosity below this level apparently allows the atomized liquid droplets to form themselves into spheres through surface tension forces prior to drying more easily and faster than more viscous liquids can attain the same shape.

Whenever carbon black is used as the pigment, it should be suspended in the desired solvent and this suspension should be added to a resin solution containing at least 10% resin to prevent shocking and consequent settling of the pigment, during blending of the suspension and solution. After this addition the liquid may then be diluted to the proper solids concentration without fear of pigment settling. This procedure was followed with all the following examples using carbon black. Other pigments than carbon black including both organic and inorganic types may be used such as chrome yellows, iron oxides, cadmium selenides, chrome greens, cobalt blues, Benzidine yellows, phthalocyanine blues and greens, etc.

The method of this invention may also be used to form two layer xerographic toners. Thus, for example, a low melting material such as a resin or wax is first dissolved in a suitable solvent and spray dried to a size close to that desired for the final xerographic toner particle size by the technique described above. This is the core of the final particle and may be pigmented with any desirable material such as carbon black, also by the technique described above. The dried particles which result from this process are, then suspended in another resin-pigmentsolvent system. This system contains a higher melting point electroscopic second resin dissolved in a solvent which will not dissolve the material used to formulate the core of the toner particle as described above and a suspended pigment. This last system is then spray dried once again so that a thin coating of the second resin including the pigment is deposited on the core material which was made as a result of the first spray drying'step. In this way, a thin, tough shell of a higher melting point electroscopic material is formed on a lower melting point core which, if used alone, might not have the proper electrical properties and would not have the physical properties necessary to withstand the wear and tear encountered in automatic xerographic copying devices. Coated toner particles of this type have been found to be advantageous especially when used in copying devices which employ heat fusing because when radiant heat from the heat fuser strikes these particles, it easily penetrates and heats up the outer surface of the particles but is much less apt to have sufiicient intensity to heat the center core of the particle above the melting point so that the whole particle will fuse onto the substrate. Accordingly, the use of a low melting point core in the toner particle compensates for the lower amount of heat which can penetrate into the center of the toner particle making for uniform fusing of the particle. Obviously, the pigment need not necessarily be included in both the core and the coating of the particle but, instead, may be included in only one of these.

In the following examples, the amount of solvent used to dissolve the resin was corrected for the amount used to suspend the pigment. Thus, if 30 ml. of solvent is used to suspend the pigment and the example calls for dissolving the resin in 400 ml. of solvent only 370 ml. was actually used for this purpose.

Example 1 A solution of 50 grams of a 65/35 styrene-n-butyl methacrylate copolymer was prepared in one liter of ethyl acetate and this solution was blended with approximately 5 grams of a suspension of carbon black in ethyl acetate. The carbon black particles had a mean diameter of approximately 13 milli-microns. It was then spray dried through an astro spray micromist ultrasonic type nozzle with a feed rate of 60 ml. per minute at p.s.i. using drying air temperatures of 160 F. input, F. output and produced dry toner particles with a. particle size ranging from 1 to 2 microns with a somewhat light gray color.

Example 2 A spray dried toner was produced by exactly the same technique as that employed with the toner of Example 2, except that the amount of carbon black suspension was doubled resulting in a much blacker toner.

Example 3 One hundred seventy six grams of the styrene-n-butyl methacrylate copolymer were dissolved in 1000 ml. of xylene in which there was suspended 25 grams of carbonyl powdered iron. This liquid was then spray dried employing a pneumatic nozzle with an air pressure of 100 p.s.i. and a feed rate of 70 ml. per minute. Drying air input temperature was 160 F. and output temperature F. Mostly spherical particles were produced with a diameter ranging from 2 to 5 microns.

Example 4 Fifty grams of a 65%-35% styrene-n-butyl methacrylate copolymer were dissolved in 1500 cc. of ethyl acetate and 1.5 grams of carbon black suspended in ethyl Fifty grams of the Example 4-copolymer were dissolved in 900 cc. of ethyl acetate. To this solution there was added 18 grams of carbon black suspended in ethyl acetate. The suspension, which had been prepared by ball milling the carbon black in the ethyl acetate in a vibrating ball mill for 2 hours, was carefully blended into the solution and then spray dried with a pneumatic nozzle operated at 100 p.s.i. air pressure at a solution feed rate of a 100cc. per minute with drying air temperatures of 200 F. input and 145 F. output. The toner particles producedwere black in color mostly spherical in shape ranging from 6 to 9 microns in size with 50% below 7 microns in diameter.

Example 6 Two hundred fifty grams of the Example 4 copolymer were dissolved in 2500 cc. of ethyl acetate and 250 grams of carbon black suspended in ethyl acetate were added to the solution. This liquid was spray dried with a pneumatic nozzle operated at a feed rate of a 150 cc. per minute and an air pressure of a 100 p.s.i. Drying air input was set at 200 F. and output drying air was 150 F. Mostly spherical black particles ranging in size from about 5 to 8 microns were produced.

Example 7 A low molecular weight polyethylene resin was dissolved in hot trichloroethylene containing suspended carbon black and spray dried into a material having an average particle size of 10. microns. These particles were then suspended in a solution of a copolymer of styrene and n-butyl methacrylate in ethyl acetate. An ethyl acetate suspension of carbon black was then added to this suspension, blended and spray dried a second time. The resultant material was a toner particle consisting of a.poly ethylene core encapsulated in a casing of the copolymer. Since "a suspension of carbonblack had been initially added to the polyethylene trichloroethylene solution, both the core and the shell of the capsule were pigmented.

Example 8 7 Example 9 Fifty grams of a 90-10 copolymer of vinyl chloride and vinyl acetate having an inherent viscosity of .80 were dissolved in 900 ml. ofrnethyl'ethyl ketone to which there was then added 15. grams of carbon black suspended in methyl ethyl ketone. After this blending the liquid was diluted to a 3% by weight solution with additional methyl ethyl ketone. The liquid was then spray dried employing .an ultrasonic nozzle of the type described in connection with Example 1, using a feed rate of 40 ml. per minute and nozzle pressureof 110 p.s.i. Input drying air temperature was 140 F. and output temperature wasrneasured at 110 F. Black spherical particles of about 1 micron in size were produced.

Example 10 3.52 parts by weight of the copolymer of Example 9 were dissolved in 100 parts by weight of methyl ethyl ketone. 0.88 part by weight of carbon black suspended in methyl ethyl ketone was then-addedto the solution and this liquid was spray dried employing a spinning disc atomizer operated at a pressure of a 100 p.s.i. and a feed rate of 55ml. per minute. Drying air input temperature was 140 F., output temperature 105 F. The tonerparticles produced were mostly spherical in shape a nd seemed tolie mostly in the5 to 6 micron diameter range. ;50% by weight of the particles were below 9.2 microns in di-' ameter. Example 11 13.7 grams of an 87/13 copolymer of vinyl chloride and vinyl acetate with an inherent viscosity of 0.50 were dissolved in 500 grams of methyl ethyl ketone. 3.55 grams of carbon black suspended methyl ethyl ketone were added to the solution by careful blending and this liquid was spray dried employing a spinning disc atomizer operated at p.s.i. and a feed rate of 45 ml. per minute. Drying air input temperature was 140 F. and output air was F. Toner particles were well pigmented, mostly spherical in shape, and for the most part ranged from 2 to 4 microns in diameter. 50% by weight of the particles were smaller than 7.0 microns in diameter.

Example 12 The same pigmented solution employed in Example 11 was made up except that 300 ml. of methyl ethyl ketone rather than 500 ml. was employed. This liquid was spray dried with the same spinning disc, atomizer, operated at 100 p.s.i., and a feed rate of 60 ml. per minute. Drying air temperatures were 140 F. input and 100 F. output. The particles were mostly 4 to 5 microns in diameter with 50% by weight of the particles being smaller than 9.0 microns in diameter.

Example 13 Ten grams of carbon black were suspended in methyl ethyl ketone and blended with a solution of 50 grams of the copolymer resin described in connection with Example 11 and 5 grams of a diphenyl phthalate plasticizer in sufficient additional methyl ethyl ketone to make 369 ml. when the suspension and solution were well blended together. The liquid was diluted by the addition of a 1000 ml. of methyl ethyl ketone. This liquid was then spray dried with a spinning disc-type atomizer at a pressure of 100 p.s.i. and a feed rate of 60 ml. per minute. Drying air input temperature was 160 F., output temperature F. The toner particles produced were black, spherical and most had diameters from 1 to 2 microns with 50% by weight of all particles being less than 9.0 microns in diameter.

Example 14 Ten grams of carbon black and 1 gram of colloidal silica available under the trade name of Cabosil from the Cabot Corporation were suspended in methyl ethyl ketone and this suspension was added to a solution of 50 grams of the copolymer described in Example 11 along with enough additional methyl ethyl ketone to make up a total of 346 milliliters, total of methyl ethyl ketone and the liquid. This liquid was spray dried with a spinning disc atomizer operated at 100 p.s.i. and'a feed rate of 60 milliliters per minute with drying air input temperatures set at F. and drying air output of 115 F. A spherically shaped toner, most of which ran-gedfrom .1 to 2 microns in diameter was produced with 50% by v Example 15 Five grams of a 27 millimicron average diameter carbon black available under the trade name'of Raven 30 from Columbian Carbon Company was suspended in methyl ethyl ketone and this suspension was added to a solution of 90 grams of a copolymer of vinyl chloride and vinyl acetate in suflicient additional methyl ethyl ketone to rnake up 600 milliliters. The copolymer consisted of 91% by weight of vinyl chloride, 3% by weight of vinyl acetate and approximately 6% of vinyl alcohol and has an inherent viscosity of .54. After blending, the liquid was diluted to 5% solids with methyl ethyl ketone and spray dried with a spinning disc atomizer at 100 p.s.i. and 90 milliliters per minute feed rate. Drying air input temperature was 117 F., output temperature 75 F. A black toner was produced with most particles ranging from 5 to 7 microns in diameter and 50% by weight of all particles below 9.0 microns.

Example 16 The same liquid formulation as in Example 15 was made up except that it was diluted down to 3% by weight of solids with methyl ethyl ketone applied to spray drying under exactly the same conditions as employed in Example 15. Black toner particles ranging from 2 to 5 microns in diameter and spherical in shape were produced with 50% by Weight of all particles below 6.8 microns.

Example 17 Ninety grams of a vinyl chloride (87% -vinyl acetate (13%) copolymer having an inherent viscosity of .28 were dissolved in 400 grams of methyl ethyl ketone. Ten grams of carbon black suspended in methyl ethyl ketone were added to the solution and carefully blended m. This liquid was then diluted to 2% solids with methyl ethyl ketone, spray dried with a spinning disc atomizer with a feed rate of 90 milliliters per minute and a pressure of 100 p.s.i. Drying air input temperature was held at 117 F. and drying air temperature was measured at 80 F. Toner particles appeared spherical under the microscope and most particles had mean diameters of from 1 to 2 microns.

Example 18 Nine parts by weight of a copolymer of methyl vinyl methyletherand maleic anhydride were dissolved in 190 parts by weight of methyl ethyl ketone and 1 gram of carbon black suspended in methyl ethyl ketone was blended into this solution. This liquid was spray dried with a spinning disc atomizer operated at 80 p.s.i. with a feed rate of 110 milliliters per minute. Drying air input temperature was set at 113 F. and drying air output temperature was measured at 76 F. This resulted in the production of small gray spherical toner particles with 50% by weight of all particles below 4.1 microns in diameter.

As stated above, any suitable natural, modified natural or synthetic resin may be used in the process of this invention. Typical synthetic resins include vinyl-type polymers having the characteristic monomeric structure: C=C and made, for example, from one or more of the following vinyl monomers: esters of saturated alcohols with mono and polybasic unsaturated acids such as alkyl acrylates and methacrylates, haloacrylates, and diethyl maleate; vinyl and vinylidene halides such as vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, and chlorotrifluoroethylene; vinyl esters such as vinyl acetate, unsaturated aromatic compounds such as styrene and various alkyl styrenes, alpha-methyl styrene parachlorostyrene, parabromostyrene, 2,4-dichlorostyrene, vinyl naphthalene, and paramethoxystyrene; unsaturated amides such as acrylamide, and rnethacrylamide; unsaturated nitriles such as acrylonitrile, methacrylonitrile; haloacrylonitrile, phenylacrylonitrile, and vinylidene cyanide; N-substituted unsaturated amides such as N,N-dimethyl acrylamide, and N-methyl acrylamide; conjugated butadienes such as butadiene and isoprene; unsaturated ethers such as divinyl ether, diallyl ether, and vinyl alkyl ether; unsaturated ketones such as divinyl ketone, and vinyl alkyl ketone; unsaturated aldehydes and acetals such as acrolein and its acetals and methacrolein and its acetals; unsaturated heterocyclic compounds such as vinyl pyridine, vinyl furan, vinyl coumarone and N-vinyl carbazole; unsaturated alicyclic compounds, such as vinyl-cyclopentane and vinyl-cyclohexane; unsaturated thio compounds such as vinyl thioethers; unsaturated hydrocarbons such as ethylene, propylene,

coumar-one, indene, terpene, polymerizable hydrocarbon fractions, and isobutylene; allyl compounds such as allyl alcohol, allyl esters, diallyl phthalate, and triallylcyanurate; as well as condensation polymers including polyesters, such as linear, unsaturated and alkyd types made, for example, by reacting a difunctional acid or anhydride such as phthalic, isophthalic, terephthalic, malic, maleic, citric, succinic, tglutaric, adipic, tartaric, pimelic, suberic, azelaic, sebacic or camphoric with a polyol such as glycerine, ethylene glycol, propylene glycol, sorbitol, mannitol, pentaerythritol, diethylene glycol or polyethylene glycol, polycarbonates such as bisphenol esters of carbonic acid; polyamides such as those made by reacting diamines with dibasic acids where the diamines contain from 2 to 10 carbon atoms and the acids contain from 2 to 18 carbon atoms; polyethers such as the epoxy type made, for example, by condensing epichlorohydrin with any one of bisphenol A, resorcinol, hydroquinone, ethylene glycol, glycerol, or other hydroxyl containing compounds; other polyethers made, for example, by reacting formaldehyde with difunctional :glycols; polyurethanes prepared, for example, by reacting a diisocyanate such as toluene-2,4- diisocyanate, methylene bis (4-phenylisocyanate), bitolylene diisocyanate, 1,5-naphthalene diisocyanate, and hexamethylene diisocyanate with a dihydroxy compound; phenol aldehyde resins made, for example, by condensing resorcinol, phenol or cresols with formaldehyde, furfural or hexamethylene tetramine; urea formaldehyde; melamine formaldehyde; polythioethers; polysulfonamides; alkyl, aryl and alkaryl silicones, etc. i

What is claimed is:

1. The method of forming finely divided, electrostatographic toner particles including an electroscopic relatively soluble resin and relatively soluble pigment particles comprising dissolving said resin in an organic relatively volatile solvent to form a resin solution, dispersing said pigment in said solution and then spray drying small droplets of said solution so that as said solvent is removed from said droplets by evaporation, resin precipitates out of solution to form small spherical toner particles including said pigment particles.

2. The method of forming colored resinous electrostatographic toner particles comprising suspending finely divided relatively insoluble pigment in a relatively volatile organic solvent solution of an electroscopic relatively soluble polymeric resin to form a suspension and then spray drying small droplets of said suspension so that as solvent is dried out of said suspension, resin precipitates out of solution to form small spherical toner particles encapsulating said pigment.

3. The method of forming colored resinous electrostatographic toner particles comprising dissolving an electrically insulating relatively soluble resin in a relatively volatile organic solvent to form a solution, suspending finely divided relatively insoluble particles of a pigment in said solution to form a suspension with said solution and then spray drying small droplets of said suspension to drive olf the volatile solvent by evaporation whereby small resin particles containing said pigment are formed.

4. The method of forming finely divided electrostatographic toner particles including an electroscopic relatively soluble resin and relatively insoluble pigment particles comprising dissolving said relatively soluble resin in an organic relatively volatile solvent to form a resin solution, suspending said relatively insoluble pigment in said solution, atomizing said solution in a gas to form gas suspended, solution droplets of a size such that the volume of the resin and pigment in each droplet is substantially equal to the volume of a toner particle of the desired size, holding each of said droplets suspended in said gas until said organic solvent is driven off from it by evaporation so that said resin precipitates out of solution to form spherical particles including said pigment and then collecting said dried particles.

. The method of forming colored, resinous, electrostatographic toner particles comprising dissolving an electroscopic relatively soluble resin in a relatively volatile organic solvent to form a resin solution, suspending a relatively insoluble pigment having a diameter no larger than one-tenth the diameter of the final toner particle to be produced in said resin solution, atomizing said solution in a gas to form gas suspended, solution droplets of a size such that the volume of the resin and pigment in each droplet is substantially equal to the volume of a toner particle of the desired size, holding each of said droplets suspended in said gas until said solvent is driven off from it by evaporation so that said resin precipitates out of solution to form a spherical particle including said pigment and then collecting the particles.

6. The method of forming finely divided electrostatographic toner particles including an electroscopic relatively soluble resin and a relatively insoluble pigment, comprising dissolving said resin in a relatively volatile organic solvent, adding said pigment to said solution to produce a spray drying liquid, the amount of solvent employed in said liquid being sufiicient so that the viscosity of said liquid is less than about 500 centipoises, and then spray drying small droplets of said liquid to drive off the solvent by evaporation so that said resin precipitates out of solution in each droplet to form a spherical particle including said pigment.

7. The method of forming finely divided electrostatographic toner particles including an electroscopic relatively soluble resin and a relatively insoluble pigment comprising dissolving said resin in a relatively volatile organic solvent to form a resin solution, dispersing said pigment in said solution and then spray drying small droplets of said solution each containing suflicient resin and pigment to form a solid particle ranging in size from 1 to 20 microns so that as solvent is removed from said droplets by evaporation, resin precipitates out of solution to form small spherical toner particles including said pigment.

8. The method of forming colored resinous electrostatographic toner particles comprising suspending finely divided carbon black pigment in a relatively volatile organic solvent, then adding said carbon black suspension to a solution of an electroscopic relatively soluble vinyltype polymer which has been dissolved in a relatively volatile organic solvent to form a suspension and then spray drying small droplets of said suspension so that as the relatively volatile organic solvent is dried out of said suspension, polymer precipitates out of solution to form small spherical toner particles encapsulating said pigment.

9. The method of forming colored, finely divided, electrostatographic toner particles including an elcctroscopic relatively soluble vinyl-type polymeric resin and a pigment which is insoluble in at least a relatively volatile organic solvent for said resin and which is smaller than one-tenth the size of the final toner particles desired comprising dissolving said resin in said solvent to form a solution, suspending said pigment in said solution to form a spray drying liquid, the amount of solvent used in said liquid being sufficient so that the viscosity of said liquid is less than about 500 centipoises, spray drying small droplets of said liquid, said droplets containing an average suflicient resin and pigment to form solid particles ranging in size from about .5 to about 30 microns so that as solvent is removed from said droplets by evaporation, resin comes out of solution to form a solid toner particle including pigment from each droplet and collecting said particles.

10. The method of forming an electrostatographic toner particle comprising dissolving a first low melting point relatively soluble resin in a relatively volatile organic solvent therefor to form a first resin solution, suspending a relatively insoluble pigment in said resin solution to form a first suspension of said pigment in said first solution, spray drying small droplets of said suspension so that as solvent is removed from said droplets by evaporation, said resin precipitates out of solution to form small spherical particles including said pigment, suspending said particles in a liquid solution of a second relatively soluble resin made with a relatively volatile organic solvent which will not dissolve said first resin, suspending additional relatively insoluble pigment particles therein and then spray drying small droplets of said suspension so that as solvent is removed from said droplet by evaporation, said dissolved resin precipitates out of solution encasing the particles made from said first resin.

11. The method of forming colored, finely-divided, electrostatographic toner particles including an electroscopic vinyl-type relatively soluble polymeric resin and a pigment which is insoluble in at least a relatively volatile organic solvent for said resin and which is smaller than one-tenth the size of the final toner particles desired comprising dissolving said resin in said solvent to form a solution, suspending said pigment in said solution to form a spray drying liquid, the amount of solvent used in said liquid being suflicient so that the viscosity of said liquid isless than about 500 centipoises, spray drying small droplets of said liquid, said droplets containing sufficient solids to form a final solid spherical toner particle of from about 1 to about 20 microns in diameter so that as solvent is removed from said droplets by evaporation, resin comes out of solution to form a solid spherical toner particle including pigment from each droplet and collecting said particles.

References Cited UNITED STATES PATENTS 2,187,877 1/1940 Ferris et al. 15948 ROBERT F. WHITE, Primary Examiner.

J. R. HALL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,338 ,991 August 29 1967 Michael A. Insalaco et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 12 line 34 for "soluble" second occurrence read insoluble Signed and sealed this 3rd day of September 1968 (SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. THE METHOD OF FORMING FINELY DIVIDED, ELECTROSTATOGRAPHIC TONER PARTICLES INCLUDING AN ELECTROSCOPIC RELATIVELY SOLUBLE RESIN AND RELATIVELY SOLUBLE PIGMENT PARTICLES COMPRISING DISSOLVING SAID RESIN IN AN ORGANIC RELATIVELY VOLATILE SOLVENT TO FORM A RESIN SOLUTION, DISPERSING SAID PIGMENT IN SAID SOLUTION AND THEN SPRAY DRYING SMALL DROPLETS OF SAID SOLUTION SO THAT AS SAID SOLVENT IS REMOVED FROM SAID DROPLETS BY EVAPORATION, RESIN PRECIPITATES OUT OF SOLUTION TO FORM SMALL SPHERICAL TONER PARTICLES INCLUDING SAID PIGMENT PARTICLES. 